General circulation, Ozone Layer and Ozone Hole

General Circulation

General Circulation of the atmosphere is related to:

1. Energy balance: It is related to the balance of incoming solar radiation and outgoing terrestrial radiation emitted by the earth.
2. Transport: Atmospheric and oceanic transport processes distribute the radiant energy equally around the earth.
3. Three cell model: This model represents the average circulation of the atmosphere and is used to describe the atmospheric transport of the energy.

The major surface weather characteristics of three cell model are:

A) Hadley cell:

The Hadley cell constitutes:

i) Doldrums: In the equatorial region from 5degree north to 5degree south latitude, pressure is generally low and so the tropical wind coverage at this intertropical convergence zone (ITCZ). The pressure gradient at this region is low so, they are light and variable. Because of convergence at ITCZ, there is an ascent of air in this region. This leads to the heavy thunder shower and precipitation in this region.

ii) Trade wind: Steady northeast wind in the northern hemisphere in between o degree to 30 degrees.

At 30 degree north, lies the subtropical high or horse latitude which separates Hadley cell and Ferrel cell. This is the region where many large deserts are found.

B. Ferrel cell:

Prevailing westerly wind: major air flow pattern of mid-latitude (30 degrees to 60 degrees N/S) from west to east direction.

C. Polar cell:

Polar easterly wind: cold polar air that is moving southwest (in the northern hemisphere) which eventually meets the prevailing westerlies to form the polar fronts.

Ozone Layer and Ozone Hole

In this region of the atmosphere from 19 to 48 km above the earth’s surface, the concentration of ozone is high, up to 10 ppm, so this region is termed as the Ozone layer. The ozone forms there by the action of sunlight on oxygen. This action has been taking place for many million years, but naturally occurring nitrogen compounds in the atmosphere apparently have kept the ozone concentration at a fairly stable level. Concentrations this great at ground level are dangerous to breathe and can damage the lungs. However, because the ozone layer of the atmosphere protects life on earth from the full force of the sun’s cancer-causing ultraviolet, it is critically important.

In the 1970s, scientists discovered that the ozone layer was being attacked by chlorofluorocarbons (CFCs), chemicals used in the refrigerator, air-conditioning systems, cleaning solvents and aerosol sprays. CFCs release chlorine into an atmosphere, which, in turn, breaks ozone down into its interaction with ozone, each chlorine molecule has the ability to destroy a large amount of ozone for an extended period of time.

The ozone hole is a term used to denote the thinned region of the ozone layer. It is predicted to cause an increase in the amount of harmful UV radiation on the earth’s surface. UV radiation causes skin cancer and cataracts in human, damage crops and to plankton. Beginning in the early 1980s, research scientists working in Antarctica have detected a periodic loss of ozone in the atmosphere high above the continent. Because of the presence of chlorine molecules in the ozone layer, the number of ozone molecule is decreasing. The decrease shows a seasonal variation.The depletion is more during the months of August to October. The deficient ozone molecules are formed in other seasons, so these seasons do not experience the ozone hole phenomena. However, a continual decrease has been observed in the ozone layer.

References:

Miller, Jr. G.T. Living in the Environment. Wadsworth Publication, 2003.

S.C., Santee. Environmental Science. India, New Center: New Center Book Agency (P) Ltd, 2004.